In humans, there is evidence that the neuropeptide vasopressin may play a role in the development and/or severity of mental health disorders characterized by aberrant social behavior, such as schizophrenia and autism spectrum disorders. The objective of this R03 application is to develop genetic tools for the exploration of the role of the vasopressin 1b receptor in species that are behaviorally rich and in which vasopressin is known to be important to the neural regulation of social behavior, specifically, Syrian hamsters and prairie voles. The proposed experiments have been designed to test the central hypothesis that across mammalian species the vasopressin 1b receptor is conserved in sequence, distribution, and function. This knowledge is relevant to the mission of the NIMH because it will further our knowledge of the neurochemistry underlying psychiatric disorders characterized by abnormal social behavior. One specific aim is proposed that is designed to determine the sequence and distribution of the vasopressin 1b receptor in Syrian hamsters and prairie voles, as well as to develop genetic tools to use in future functional studies. The proposed research is significant because by determining how conserved the vasopressin 1b system is and how it modulates social behavior and our understanding of the vasopressin system in humans can be improved.